Master of Science, The Ohio State University, 2020, Earth Sciences

The depth of magma storage beneath volcanoes has been a primary focus of recent geophysical and petrological research. Investigation of magma plumbing systems has important implications for volcanic hazard mitigation and eruption forecasting, and also for our understanding of the origin and evolution of magmas. This work is particularly important at mid-ocean ridges, as they are responsible for the formation of the majority of Earth's crust. Previous petrologic studies of mid-ocean ridges have suggested that olivine-plagioclase-clinopyroxene-liquid cotectic crystallization begins at mantle depths, which has far-reaching implications for our understanding of the mechanisms for crustal accretion. We demonstrate a procedure for processing pressure results using the Kelley & Barton (2008) geobarometer, which significantly changes the interpretation of these results. This process allows for high-resolution interpretation of the pressures, and thus depths, of partial crystallization in mafic systems. Application of this approach to data from the Juan de Fuca Ridge suggests that olivine-plagioclase-clinopyroxene-liquid cotectic crystallization occurs within the crust, and not in the mantle as suggested previously. The results suggest that partial crystallization along the ridge is polybaric. In the southern portion of the ridge, seismically imaged melt lenses are within range of the calculated pressures, however, the average pressures suggest that the majority of olivine-plagioclase-clinopyroxene-liquid cotectic crystallization occurs at greater depths than the imaged melt lenses. This suggests multi-depth magma storage along much of the Juan de Fuca Ridge, with only the shallowest magma reservoirs being imaged by seismic studies.

Committee: Michael Barton (Advisor); Daniel Kelley (Committee Member); Thomas Darrah (Committee Member); Elizabeth Griffith (Committee Member) Subjects: Geology; Petrology

Doctor of Philosophy, Miami University, 2017, Geology and Environmental Earth Science

The first project investigates diverse magmas erupted over the 35 ky known history of Hayes Volcano in south-central Alaska. Three distinct magma types are delineated. Two of these have adakite-like compositions (elevated Sr/Y and depleted heavy rare earth elements) while the other is non-adakitic. These magmas are modeled to be products of fractional crystallization accompanied by assimilation of diverse materials best explained by varying ascent pathways and polybaric differentiation from the same mantle source. Their generation is directly controlled by the geometry of the Pacific Plate beneath Hayes. Additionally, shared isotopic and trace element compositions of Hayes and Mount Spurr define a common mantle source. This study provides new insights into the production of varied magmas along the Aleutian-Alaskan arc. The second project tests the feasibility of tracing past uranium (U) contamination in the growth rings of trees. Like other metals, U mobility in annual growth rings is dependent on the tree species. Uranium abundances and isotopic compositions were measured in sugar maple, black walnut, slippery elm, and white ash tree rings near the former Fernald Feed Materials Production Center (FFMPC), a U purification facility in Ohio. U concentrations, 235U/238U, and 234U/238U in sugar maple are generally consistent with known events in FFMPC history suggesting that this species is reliable for monitoring past U contamination. However, U isotopic compositions (including 236U/238U) do not correspond to known events in black walnut, slippery elm, and white ash tree rings; therefore, U must be mobile across annual growth rings in these species. Nevertheless, the youngest growth rings in sugar maple and slippery elm are isotopically similar to contemporary soil compositions suggesting that these species may be used to monitor current, bioavailable U contamination. The final project uses lichen to trace the spatial extent of past, cryptic airborne industrial a (open full item for complete abstract)

Committee: William Hart (Advisor); Elisabeth Widom (Advisor); John Rakovan (Committee Member); Neil Danielson (Committee Member); Darin Snyder (Committee Member) Subjects: Environmental Geology; Environmental Science; Geochemistry; Geological; Geology

Master of Science (MS), Bowling Green State University, 2011, Geology

Sediments recovered between ~354 and 765 mbsf (~15.9-18.4 Ma) in the ANDRILL AND-2A core contain dispersed accumulations of volcanic glass up to 50% by volume and are used to investigate the petrological evolution and influence of glaciations on volcanism in the McMurdo Sound region of Antarctica. Glass-rich sediments include muddy-to-fine sandstone and stratified diamictite. The glass varies in color, size, vesicularity, crystal content, angularity, and from fresh to moderately altered. Fresh glass with delicate cuspate forms suggests they were introduced into the basin as ash fall with minimal reworking. Altered glass has low total oxides (< 97 wt.%), low Ca/K ratios (< 2), high Alteration Index (> 40), and are typically more evolved than fresh glass. Pristine basaltic glasses (MgO 3-7 wt.%) are ne-normative (5-30 wt.%) and have restricted average SiO2 content (45.2 ± 0.8 wt.%). Overall the glass composition shows an increase in SiO2 content up-section. Fractional crystallization models indicate differentiation controlled by plagioclase, olivine, clinopyroxene and magnetite ± amphibole and apatite. Trace element concentrations are typical for Erebus Volcanic Province (EVP) volcanism. The data extends known composition of Mount Morning (18.7-11.4 Ma), the only known EVP Early-Middle Miocene source, to a mafic end, revealing a previously unknown phase of explosive, strongly alkaline, basaltic activity. The glass-rich sediments are part of larger sequences that record numerous glacial advances and retreats in the region. Sediments with high glass contents correspond to ice minimums and, geochemically, Ba/LREE ratios correlate to intervals of ice expansion (decreasing values) and contraction (increasing values) at multiple depths. Higher Ba/LREE may indicate tapping of more volatile-rich magmas. Within a single glacimarine cycle, glass angularity, vesicularity and composition also vary systematically. A model is supported where ice loading and unloading affects the st (open full item for complete abstract)

Committee: Kurt Panter PhD (Advisor); John Farver PhD (Committee Member); Jeffrey Snyder PhD (Committee Member) Subjects: Geology